The invention relates to a device for absorbing and/or attenuating sound waves with a sound wave absorbing and/or attenuating system using a thin vibratable layer on the side facing the incident sound waves.
Such a device is known in the art (DE-OS 33 13 001). This device is formed by a porous base provided with projecting areas so as to create hollow chambers, which are covered by a foil having a layer thickness of preferably 30 .mu.m, which is placed over the projecting areas. The porous base acts as a sound absorber for the higher frequencies while the foil is a membrane absorber for the lower frequencies.
Other devices with sound wave absorbing and/or attenuating systems are known (EP-0 454 949 A2, DE Utility Model 92 15 132). In these devices, porous nonwovens or open-cell foam, particularly made of polypropylene, are formed so as to create so-called Helmholtz resonators together with a substrate or the engine hood. In one of these embodiments, a polyurethane foil covers the chamber system extending, respectively, along the foam walls forming the chambers.
DE-OS 36 01 204 furthermore discloses a method for forming packing units made of plastic fiber material and highly heat resistant inorganic fiber material, for example basalt fibers, to be used as a sound attenuating lining for the engine compartment of motor vehicles and partly laminating these packing units with a heat reflecting aluminum foil on the side facing the engine.
Finally, it is known in the art (EP-0 439 046 A2, GB Patent 482 747) to arrange aluminum sheets along the exterior of packing units, which are made of corrugated metal layers, to create reflecting heat shields for components that are exposed to flames.